A high school classmate turned personal attorney of Robert Durst said Wednesday that the New York real estate mogul hadn’t seemed concerned years earlier when he’d called him to say his wife had disappeared.

Stewart Altman testified during a Los Angeles court hearing that his friend’s demeanor on the phone seemed strange, but said he did not suspect that Durst had killed his wife.

Altman testified that he recalled getting a phone call from Durst in 1982 saying that his wife had gone missing. The witness said he did not offer to call the police or call around to hospitals, because he “didn’t think it would help.”

“Because you knew she was dead?” the prosecutor shot back.

“No,” Altman said, drawing out his denial for emphasis.

“Did he sound concerned?” the prosecutor asked of Durst’s phone call.

“No,” Altman responded.

“Did that seem strange to you?”

“Yes.”

Durst has lived under suspicion since his wife, Kathleen, disappeared in 1982. Prosecutors contend that Durst killed her.

But it is because of the 2000 slaying of his confidante Susan Berman that Durst now awaits trial in Los Angeles on a first-degree murder charge. Prosecutors argue that the killing was meant to silence Berman for what she knew about Kathleen Durst’s disappearance.

The 74-year-old millionaire has pleaded not guilty and told a judge he did not kill Berman. The sensational case is not scheduled to go to trial until at least 2018. In the meantime, a judge has allowed prosecutors and defense attorneys to question Altman and his wife, Emily, as well as other elderly witnesses to preserve their testimony.

At one point, a prosecutor displayed a photocopy of an anonymous note sent to police around the time of Berman’s death alerting them to a “cadaver” inside her home. It read: “1527 BENEDICT CANYON CADAVER.”

Asked if the handwriting looked like Durst’s, the witness said, “It’s possible.” When a prosecutor pressed the question, Stewart Altman said it looked “similar” to Durst’s handwriting.

His testimony mirrored that of Emily Altman, who testified at a hearing last month that the handwriting looked like that of Durst.

During Wednesday’s hearing, Stewart Altman testified that Durst is an intelligent, witty person, who struggles to relate to others and show emotion. Durst listened to the exchange through voice-amplifaction earphones and stared…